The present invention relates generally to gas and steam turbines, and, more specifically, to rotor seals therein.
In a gas turbine engine, air is pressurized in a multistage compressor and mixed with fuel in a combustor for generating hot combustion gases. The gases flow through turbine stages which extract energy therefrom for providing output power, such as powering an electrical generator joined thereto.
In a steam turbine, hot pressurized steam is separately formed in a steam boiler and channeled to steam turbine stages which extract energy therefrom for producing output power, such as powering an electrical generator.
Both types of turbine engines include rotors which are driven by the hot pressurized gases as they are expanded in the turbines thereof. The rotor includes various disks from which extend radially outwardly rotor blades or buckets which cooperate with stationary nozzles or diaphragms which include stator vanes between which gases are channeled. The rotor disks are interconnected by a rotor shaft suitably mounted in bearings.
In the gas turbine engine, the turbine rotor is also joined to the compressor rotor from which extend compressor rotor blades for pressurizing air during operation. And, in the steam turbine engine, the rotor disks are arranged in groups for defining a high pressure turbine, an intermediate pressure turbine, and a low pressure turbine all joined together in an exemplary configuration for powering the generator.
Each compression stage in the gas turbine, and each turbine stage in the gas and steam turbines requires suitable sealing to ensure that the pressurized gas or fluid is channeled between the stator vanes and rotor blades with minimal leakage for maximizing efficiency of operation. Since gas and steam turbine engines are typically manufactured for long useful lives, the seals therein should also be configured for long useful lives and reducing the need for maintenance or repair thereof which requires taking the corresponding machine off-line, and therefore interrupting power generation.
Various forms of seals are provided in these different types of machines and are located at various positions between stator and rotor components. The seals must be specifically configured for effective operation for various differential pressures depending upon their location in the machine. Low pressure seals are simpler in construction than high pressure seals, and the corresponding design requirements therefor are different. Differential pressures ranging from a few psi to a couple of thousand psi in these turbine machines are common, and require suitably configured seals for effective operation and longevity.
Two types of the many seals used in gas and steam turbine machines include the labyrinth seal and the brush seal. The labyrinth seal includes a sharp tooth, typically an array of teeth, which are disposed between stator and rotor components for providing a seal therebetween with a relatively small radial gap to reduce tooth damage during occasional tip rubs. A brush seal, having an array of bristles, is mounted between the stator and rotor components in a friction fit therebetween for providing sealing thereat.
Both types of seals are subject to eccentric orbiting of the rotor shaft during transient operations such as start up or shutdown of the turbine as the turbine rotors pass through various critical speeds or rotational frequencies. At steady-state operation at constant speed for powering the generator, the rotors rotate true with little if any deviation or orbiting from the rotor centerline axis.
Accordingly, transient orbiting of the rotor causes the rotor to deflect toward the surrounding seal and therefore introduce undesirable rubbing loads therein. In the case of the labyrinth teeth, tip rubs thereof will cause damage thereto and dull the otherwise sharp teeth which reduces the sealing efficiency thereof. And, tip rubs correspondingly increase the nominal radial clearance or gap between the teeth and the rotor and reduce the sealing effectiveness of the labyrinth seal.
Correspondingly, transient orbiting of the rotor within a brush seal can accelerate bristle wear, which can shorten useful seal life and reduce sealing effectiveness. Furthermore, the seals are also subject to differential thermal expansion and contraction movement with the rotor during transient operation which can also cause undesirable rubbing therebetween.
In view of the substantial number of rotor seals in the gas turbine engine or in the steam turbine machine, damage thereto during transient machine operation significantly affects the useful life thereof and sealing performance. The seals are found at various locations between stator components and the rotor shafts, between nozzles or diaphragms and the rotors, between blade or bucket tips and surrounding stator shrouds, and at various supporting bearings along the rotor shafts.
Accordingly, it is desired to provide an improved rotor seal assembly for gas and steam turbine machines for accommodating transient movement of the rotor shafts therein.